Gathering information about well conditions is something that is of vital importance in the oil and gas industry, and well known. However, gathering and transferring information from below barriers in a borehole, such as below plugs or valves, can be challenging.
Solutions to the problem exist. U.S. Pat. No. 7,301,472B2 proposes to transfer signals past obstructions in a borehole acoustically by use of a tubing string.
U.S. Pat. No. 6,912,177B2 describes transmitting data in a borehole past an obstruction by sending sonic signals along an elongated tubular member, by sending it from a first side of a physical obstruction to a second side of the obstruction, where the second side is located a short distance from the first side. The signal will be received by a receiver on the second side of the obstruction, where it will be stored for later retrieval.
Both the referenced patents relate to transmission of signals along an elongate tubular member, such as a drill string, with particular adaptions made to the tubular member prior to lowering into a borehole. Neither of the referenced patents provide a solution for transferring signals past a barrier set in a tubular permanently fixed to the surroundings where such adaptions may not be possible.
An acoustic signal may propagate either as a body wave or as a surface wave in an elastic medium with rigidity, such as iron or steel. Surface waves contain little energy and are quickly absorbed by the body's surroundings and are therefore of little use to propagate a signal over a useful distance. Surface waves are often used in ultrasonic inspection equipment.
Body waves are of two types: Primary waves (also called P-waves or pressure waves) and Secondary waves (S-waves or shear waves).
In a body wave, the acoustic energy is transferred as a longitudinal wave (P-wave) or as a transverse wave (S-wave) through an elastic medium with rigidity. P-waves may also propagate in liquid or gaseous materials, where S-waves only propagate in solid materials, as shear forces.
A P-wave is a body wave that moves particles within the body back and forth in the same direction and in the opposite direction as the direction the wave is forming and is formed by alternating compressions and rarefactions. An S-wave is a body wave that shakes the body back and forth perpendicular to the direction the wave is moving. The S-wave's energy thus quickly dissipates to the surroundings.
US2005/0121253A1 discloses a telemetry system having: a pipe; a SCADA box acoustically coupled to the pipe; and a gauge inserted in the pipe. The gauge comprises: an acoustic wave generator; a coupler mechanically connected to the acoustic wave generator. The coupler is engageable and disengageable with the pipe, and the coupler defines an acoustic transmission path between the acoustic wave generator and the pipe when engaged with the pipe. The gauge further comprises a signal controller in communication with the acoustic wave generator. Further is disclosed a method for communicating information in a wellbore from a downhole location to the surface, the method having the following steps: running a downhole gauge into a pipe within the wellbore, wherein the downhole gauge comprise an acoustic wave generator; setting the downhole gauge in the pipe; and communicating an acoustic signal between the downhole gauge and the pipe.